Locating method of an optical sensor, an adjustment method of dot printing position using the optical sensor, and a printing apparatus

Abstract

There is provided a printing registration method for stably performing printing registration in bi-directional scanning by a print head in a printing apparatus or printing registration between a plurality of print heads with high accuracy. In complementary printing by the bi-directional scanning by the head, a plurality of patterns are printed while printing starting timings are shifted by predetermined quantities with respect to reference dots (dots formed by forward scanning). In the pattern, an area factor defined by the dots formed by the printing is varied according to the shifting. The plurality of patterns are optically read as an average density. The timing corresponding to a point where the read average density is highest can be determined as a printing registration condition. Furthermore, an optical sensor used for the reading is located at a position where an S/N ratio is stable with respect to fluctuations in distance from the object to be read, thus achieving stable reading.

What is claimed is:  
     
       1. An optical sensor locating method comprising the steps of: 
       providing an optical sensor comprising a light-emitting portion for irradiating an object to be measured with light and a photosensing portion for sensing the light reflected on the object to be measured; and  
       locating the optical sensor at a position where an output characteristic of the optical sensor is substantially stable with respect to factors of fluctuations at a time of measurement relative to the object to be measured,  
       wherein, the factors of fluctuations are fluctuations in distance between the object to be measured and the optical sensor; and  
       wherein, the position at which the optical sensor is located is determined in relation to the distance from the object to be measured and on the basis of an S/N ratio as the output characteristic of the optical sensor.  
     
     
       2. An optical sensor locating method as claimed in  claim 1 , wherein a center value of the fluctuations in distance is set at a value of a distance longer by a predetermined quantity than a distance where the S/N ratio is maximum. 
     
     
       3. An optical sensor locating method as claimed in  claim 1 , wherein the output characteristic of the optical sensor varies in accordance with the distance from the object to be measured, and the output characteristic of the optical sensor includes a first area where the output characteristic significantly varies in relation to a variation of the distance from the object to be measured, and a second area where a varying of the output characteristic relating to a variation of the distance from the object to be measured is smaller than that of the first area, wherein, the position at which the optical sensor is located is a position corresponding to the second area. 
     
     
       4. A printing registration method for performing printing registration in a first printing operation and a second printing operation of a printing apparatus that prints an image by said first printing operation and said second printing operation with predetermined conditions of a dot forming position on a printing medium by using a printing head, said method comprising the steps of: 
       pattern-forming for controlling said printing head to form a plurality of patterns respectively having optical characteristics corresponding to a plurality of shifting amounts, said plurality of patterns being respectively formed corresponding to said plurality of shifting amounts of relative printing positions of said first printing operation and said second printing operation, said plurality of patterns being formed by said first printing operation and said second printing operation;  
       measuring respective optical characteristics of said plurality of formed patterns by using an optical sensor comprising a light-emitting portion for irradiating said patterns as an object to be measured with light and a photosensing portion for sensing the light reflected on the object to be measured, said optical sensor being located at a position where an output characteristic of the optical sensor is substantially stable with respect to factors of fluctuations at the time of measurement relative to the object to be measured, wherein, the factors of fluctuations are fluctuations in distance between the object to be measured and the optical sensor, and wherein the position at which the optical sensor is located is determined in relation to the distance from the object to be measured and on the basis of an S/N ratio as the output characteristic of the optical sensor; and  
       acquiring an adjustment value of a dot forming position condition between said first printing operation and said second printing operation on the basis of respective optical characteristics of said plurality of patterns measured.  
     
     
       5. A printing registration method as claimed in  claim 4 , wherein a center value of the fluctuations in distance is set at a value of a distance longer by a predetermined quantity than a distance where the S/N ratio is maximum. 
     
     
       6. A printing registration method as claimed in  claim 4 , wherein said first printing operation and said second printing operation include at least one of a printing operation in a forward scan and a printing operation in a reverse scan respectively upon performing printing by bi-directional scanning of said printing head with respect to said printing medium, a printing operation being a printing by a first printing head and a printing by a second printing head among a plurality of said printing heads respectively in a direction in which said first printing head and said second printing head are relatively scanned with respect to said printing medium, and a printing operation being a printing by a first printing head and a printing by a second printing head among a plurality of printing heads respectively, in a direction different from the direction which said first printing head and said second printing head are relatively scanned with respect to said printing medium. 
     
     
       7. A printing registration method as claimed in  claim 4 , wherein said adjustment value acquiring step derives said adjustment value by a calculation employing continuous values on the basis of optical characteristics data obtained from said measuring step by using a linear approximation or a polynominal approximation. 
     
     
       8. A printing registration method as claimed in  claim 4 , wherein, in said pattern-forming step, dots formed by said first printing operation and dots formed by said second printing operation are arranged, and a relative positional relationship of said dots is varied corresponding to said plurality of shifting amounts, and a ratio of said dots covering said printing medium is varied, thereby to form said plurality of patterns having optical characteristics corresponding to said shifting amounts. 
     
     
       9. A printing registration method as claimed in  claim 4 , wherein said printing head is a head for performing printing by ejecting ink. 
     
     
       10. A printing registration method as claimed in  claim 7 , wherein said printing head has heating elements for generating thermal energy to make the ink film-boil as an energy used for ejecting the ink. 
     
     
       11. A printing registration method as claimed in  claim 4 , wherein the output characteristic of the optical sensor varies in accordance with the distance from the object to be measured, and the output characteristic of the optical sensor includes a first area where the output characteristic significantly varies in relation to a variation of the distance from the object to be measured, and a second area where a varying of the output characteristic relating to a variation of the distance from the object to be measured is smaller than that of the first area, wherein, the position at which the optical sensor is located is a position corresponding to the second area. 
     
     
       12. A printing apparatus for performing printing of an image on a printing medium by using a printing head, said printing apparatus comprising: 
       means for measuring an object by using an optical sensor comprising a light-emitting portion for irradiating the object to be measured with light and a photosensing portion for sensing the light reflected on the object to be measured; and  
       means for locating said optical sensor at a position where an output characteristic of the optical sensor is substantially stable with respect to factors of fluctuations at the time of measurement relative to the object to be measured,  
       wherein, the factors of fluctuations are fluctuations in distance between the object to be measured and the optical sensor; and  
       wherein, the position at which the optical sensor is located is determined in relation to the distance from the object to be measured and on the basis of an S/N ratio as the output characteristic of the sensor.  
     
     
       13. A printing apparatus as claimed in  claim 12 , wherein a center value of the fluctuations in distance is set at a value of a distance longer by a predetermined quantity than a distance where the S/N ratio is maximum. 
     
     
       14. A printing apparatus as claimed in  claim 12 , wherein the output characteristic of the optical sensor varies in accordance with the distance from the object to be measured, and the output characteristic of the optical sensor includes a first area where the output characteristic significantly varies in relation to a variation of the distance from the object to be measured, and a second area where a varying of the output characteristic relating to a variation of the distance from the object to be measured is smaller than that of the first area, wherein, the position at which the optical sensor is located is a position corresponding to the second area. 
     
     
       15. A printing apparatus for performing printing of an image by a first printing operation and a second printing operation with predetermined conditions of a dot forming position on a printing medium by using a printing head, said printing apparatus comprising: 
       pattern-forming means for controlling said printing head to form a plurality of patterns respectively having optical characteristics corresponding to a plurality of shifting amounts, said plurality of patterns being respectively formed corresponding to said plurality of shifting amounts of relative printing positions of said first printing operation and said second printing operation, said plurality of patterns being formed by said first printing operation and said second printing operation;  
       means for measuring respective optical characteristics of said plurality of formed patterns by using an optical sensor comprising a light-emitting portion for irradiating said pattern as an object to be measured with light and a photosensing portion for sensing the light reflected on the object to be measured, said optical sensor being located at a position where an output characteristic of the optical sensor is substantially stable with respect to factors of fluctuations at the time of measurement relative to the object to be measured, wherein, the factors of fluctuations are fluctuations in distance between the object to be measured and the optical sensor, and wherein, the position at which the optical sensor is located is determined in relation to the distance from the object to be measured and on the basis of an S/N ratio as the output characteristic of the optical sensor; and  
       means for acquiring an adjustment value of a dot forming position condition between said first printing operation and said second printing operation on the basis of respective optical characteristics of said plurality of patterns measured.  
     
     
       16. A printing apparatus as claimed in  claim 15 , wherein center value of the fluctuations in distance is set at a value of a distance longer by a predetermined quantity than a distance where the S/N ratio is maximum. 
     
     
       17. A printing apparatus as claimed in  claim 15 , wherein said first printing operation and said second printing operation include at least one of a printing operation in a forward scan and a printing operation in a reverse scan respectively upon performing printing by bi-directional scanning of said printing head with respect to said printing medium, a printing operation being a printing by a first printing head and a printing by a second printing head among a plurality of said printing heads respectively in a direction in which said first printing head and said second printing head are relatively scanned with respect to said printing medium, and a printing operation being a printing by a first printing head and a printing by a second printing head among a plurality of printing heads respectively, in a direction different from the direction which said first printing head and said second printing head are relatively scanned with respect to said printing medium. 
     
     
       18. A printing apparatus as claimed in  claim 15 , wherein said adjustment value acquiring means derives said adjustment value by a calculation employing continuous values on the basis of optical characteristics data obtained from said measuring means by using a linear approximation or a polynominal approximation. 
     
     
       19. A printing apparatus as claimed in  claim 15 , wherein, in the pattern forming by said pattern-forming means, dots formed by said first printing operation and dots formed by said second printing operation are arranged, and a relative positional relationship of said dots is varied corresponding to said plurality of shifting amounts, and a ratio of said dots covering said printing medium is varied, thereby to form said plurality of patterns having optical characteristics corresponding to said shifting amounts. 
     
     
       20. A printing apparatus as claimed in  claim 15 , wherein said printing head is a head for performing printing by ejecting ink. 
     
     
       21. A printing apparatus as claimed in  claim 20 , wherein said printing head has heating elements for generating thermal energy to make the ink film-boil as an energy used for ejecting the ink. 
     
     
       22. A printing apparatus as claimed in  claim 15 , wherein the output characteristic of the optical sensor varies in accordance with the distance from the object to be measured, and the output characteristic of the optical sensor includes a first area where the output characteristic significantly varies in relation to a variation of the distance from the object to be measured, and a second area where a varying of the output characteristic relating to a variation of the distance from the object to be measured is smaller than that of the first area, wherein, the position at which the optical sensor is located is a position corresponding to the second area. 
     
     
       23. A printing system provided with a printing apparatus for performing printing of an image by a first printing operation and a second printing operation with predetermined conditions of a dot forming position on a printing medium by using a printing head, and a host apparatus for supplying image data to said printing apparatus, comprising: 
       pattern-forming means for controlling said printing head to form a plurality of patterns respectively having optical characteristics corresponding to a plurality of shifting amounts, said plurality of patterns being respectively formed corresponding to said plurality of shifting amounts of relative printing positions of said first printing operation and said second printing operation, said plurality of patterns being formed by said first printing operation and said second printing operation;  
       means for measuring respective optical characteristics of said plurality of formed patterns by using an optical sensor comprising a light-emitting portion for irradiating said pattern as an object to be measured with light and a photosensing portion for sensing the light reflected on the object to be measured, said optical sensor being located at a position where an output characteristic of the optical sensor is substantially stable with respect to factors of fluctuations at the time of measurement relative to the object to be measured, wherein, the factors of fluctuations are fluctuations in distance between the object to be measured and the optical sensor, and wherein, the position at which the optical sensor is located is determined in relation to the distance from the object to be measured and on the basis of an S/N ratio as the output characteristic of the optical sensor; and  
       means for acquiring an adjustment value of a dot forming position condition between said first printing operation and said second printing operation on the basis of respective optical characteristics of said plurality of patterns measured.  
     
     
       24. A printing system as claimed in  claim 23 , wherein the output characteristic of the optical sensor varies in accordance with the distance from the object to be measured, and the output characteristic of the optical sensor includes a first area where the output characteristic significantly varies in relation to a variation of the distance from the object to be measured, and a second area where a varying of the output characteristic relating to a variation of the distance from the object to be measured is smaller than that of the first area, wherein, the position at which the optical sensor is located is a position corresponding to the second area.